The present invention relates generally to rotating compression equipment. More particularly, the present invention relates to devices to prevent the reverse rotation of compression equipment. Still more particularly, the present invention relates to devices to prevent reverse rotation by directly engaging the driveshaft of a centrifugal compressor.
In general, rotating compression equipment, such as compressors and pumps, is used to increase the pressure of a fluid in order to move fluid from one point to another or to provide a supply of pressurized fluid. The compression equipment creates a suction effect at its inlet that draws in fluid so that work can be performed on the fluid. Once pressurized, fluid can be discharged to other equipment, compressed further, used immediately, or stored in an accumulator for later use. Rotating compression equipment generally utilizes a rotating element, usually comprising a shaft and impellor or rotor, as a means to compress a fluid. Rotating pumps include centrifugal or radial flow pumps, axial flow or propeller pumps, etc. Rotating compressors include centrifugal compressors, axial or in-line compressors, scroll compressors, etc.
Reverse rotation in rotating compression equipment can occur when the rotating equipment is shut down, intentionally or unintentionally, such as when there is a power interruption. When power is no longer provided to rotate the driveshaft, the rotating components of the compression equipment are free to move in response to pressure differentials existing between the inlet and outlet. There is a tendency for the compressed fluid stored in the accumulator and compressed fluid in the compressor outlet to backflow. If unimpeded, the backflow of the compressed fluid will exert a force on the impellor(s), which may result in reverse rotation of the rotating components. Although reverse rotation is commonly caused by the backflow of compressed fluid, in certain equipment that is driven by an electric motor, reverse rotation can also be caused by unintentionally connecting the electric motor leads backwards.
Although the reverse rotation may be of short and transient duration, there are numerous negative consequences of reverse rotation. Reverse rotation may result in objectionable noise and vibration. Further, lubrication systems may not be designed to operate under reverse rotation conditions, or may operate poorly under reverse rotation conditions. Failure of the lubrication system may result in unnecessary wear and physical damage to various parts. Still further, drive mechanisms, such as bearings, gears, and pinions, may not be designed to operate under reverse rotation conditions, or may operate poorly under reverse rotation conditions. Such bearings, gears, and pinions may also suffer unnecessary wear and physical damage under reverse rotation conditions. Still further, in the case where reverse rotation is taking place and the equipment suddenly regains power, the abrupt application of torque to the drive shaft opposite the direction of reverse rotation may result in extremely high stresses in the drive mechanisms (e.g., driveshaft, gears, pinions, etc.). These stresses may be significantly larger than stresses under normal operating conditions and may actually result in the physical breaking of certain components.
Damage to the certain components by unnecessary wear, physical breakage, or other negative consequences of reverse rotation may necessitate a complete shutdown and repair of the compression equipment. The downtime required to repair damages cause by reverse rotation may be very lengthy and costly.
Thus, there remains a need to develop methods and apparatus for more reliable means to prevent reverse rotation of a compressor, which overcome some of the foregoing difficulties while providing more advantageous overall results.